Plastic pipes can be made by helically winding a plastic strip having series of spaced apart upstanding ribs extending longitudinally. This form of helically wound tube or pipe is already known in the piping industry and is described in patents by the applicant relating both to the form of the plastic strip and to the form of the machine by means of which the pipes or tubes are produced from such strips.
In the past, in order to create high performance pipes it was necessary for the wall thickness of the plastic strip and its ribs to be quite substantial. However, the applicant's Australian Patent No. 2003227090 disclosed an important advance in helically wound pipes. The composite strip disclosed by Patent No. 2003227090 includes an elongate reinforcing strip extending lengthwise and supported laterally by a rib portion (see FIG. 1). The reinforcing strip has a height to thickness ratio of at least 3 to 1 and is orientated substantially perpendicular to the base of the strip. With this composite strip, a stiff pipe, able to withstand significant radial crushing forces can be produced without the need for a strip having a thick plastic base and thick ribs (see FIG. 2 for instance).
When a composite strip, such as the strip described in the applicant's Australian Patent No. 2003227090, or another functionally similar strip, is wound on to a spool for transport after manufacture, difficulties may be encountered. In particular, where the composite strip has been designed for a large diameter pipe, often it is desirable to wind the strip on to a spool having a hub with a diameter substantially less than that of the final wound pipe. It has been found that this can create problems relating to the stability of the reinforcing portion within the composite strip. More specifically, there can be a tendency for the ribs of the composite strip to collapse sideways towards the base as is shown in the background drawings of FIGS. 4, 5, 6 and 7.
Another problem with spooling composite strip of the type discussed above is that if conventional spooling methods and apparatus are used, the tension in the strip becomes so high that the strip is crushed or otherwise damaged in the spooling process.
It is an object of the present invention to provide an apparatus and method that address or at least ameliorates some or all of the afore-mentioned problems